Keywords
minimally invasive cardiac surgery, minimally invasive mitral valve replacement
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Mitral valve dysfunction is a common pathologic process. The process may involve any component of the valve or subvalvular structures, including the valve leaflets, the annulus, the papillary muscles, the chordae tendineae, and the left ventricular wall.
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The anatomic description of the mitral valve is best visualized using a three-dimensional approach to its location in the heart. The anterior portion of the mitral valve annulus is positioned posterior to the aortic annulus and is bordered by the left and right fibrous trigones. The atrioventricular (AV) node and the bundle of His are adjacent to the right trigone. The circumflex artery runs along the posterior annulus of the mitral valve and may be at risk during mitral valve repair or replacement ( Fig. 20.1 ).
Figure 20.1
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Chordae tendineae extend from the anterior and posterior papillary muscles to both leaflets. Primary chordae attach to the free margin of the leaflet, whereas secondary chordae attach to the middle and posterior aspects of the leaflets closer to the annulus.
Step 1
Preoperative Considerations
1
Indications
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Most common indications for mitral valve replacement are rheumatic mitral stenosis and infective endocarditis. Replacement is less commonly performed for degenerative disease and functional mitral regurgitation.
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Mitral valve repair is indicated in those with severe myxomatous disease with the presence of gross redundancy of both anterior and posterior leaflets, especially in the younger population. In older adults, mitral regurgitation usually is a result of fibroelastic deficiency disease.
2
Operative Risk
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Long-standing, severe mitral stenosis results in pulmonary hypertension, right ventricular dysfunction, and a variable degree of tricuspid valve regurgitation. If severe, this can result in secondary hepatic and renal dysfunction, with a resultant increase in operative risk.
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Mitral annular calcifications are frequently present in older adults, especially in cases of rheumatic mitral stenosis. Calcifications typically involve the posterior aspect of the mitral annulus and can extend to the base of the posterior leaflet and the base of the left ventricle. Severe calcification of the mitral annulus appears as a horseshoe sign on the preoperative chest radiograph or coronary angiogram ( Fig. 20.2 ).
Figure 20.2
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Standard preoperative assessment of mitral valve disease is performed by transthoracic or transesophageal echocardiography. Transesophageal echocardiography allows more precise assessment of the anatomy and function of the mitral valve and represents the gold standard in preoperative assessment and planning of the operation. It is an essential tool intraoperatively for assessment of the valve repair or replacement after weaning from cardiopulmonary bypass.
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Mechanical prostheses are indicated for patients younger than 65 years; biologic valves are used more commonly in older adults. This paradigm may shift as the valves evolve in quality and durability, along with the possibility of the use of catheter-based prostheses.
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Selection of the surgical approach depends on the cause of the mitral valve disease, the presence of concomitant coronary or valvular disease, body habitus, and anatomic chest wall deformities.
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Most patients who require isolated mitral valve surgery are candidates for a minimally invasive approach. Relative contraindications to a minimally invasive approach include morbid obesity and extensive mitral annular calcifications.
Step 2
Conduct of the Operation
1
Incision
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The standard incision for minimally invasive mitral valve repair or replacement is a 6- to 8-cm skin incision and a partial upper sternotomy, extending to the left fourth intercostal space. This approach is described in detail in this chapter ( Fig. 20.3 ).
Figure 20.3
2
Dissection
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A small sternal retractor with removable blades (Baxter Healthcare, Deerfield, IL) is used to retract the sternum before proceeding with the dissection. The thymic remnants are divided and ligated with nonabsorbable sutures, and the upper pericardium is divided along the midline.
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The retractor is then removed and a pericardial sac is formed by placing stay sutures in the skin using 2-0 silk sutures. Transient hypotension may occur when the edges of the pericardium are pulled up and toward the skin owing to the displacement of the superior mediastinum and an associated decrease in venous return to the right atrium.
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The sternal retractor is reinserted to expose the great vessels and the right atrium. Cardiopulmonary bypass is initiated by cannulation of the ascending aorta and the superior and inferior venae cavae. The ascending aorta is cannulated by a flexible aortic cannula (21 F), whereas bicaval cannulation is accomplished by placing flexible venous cannulae (24 F) into the distal superior vena cava (SVC) and through the right atrial appendage into the inferior vena cava (IVC). Vacuum-assisted venous drainage is used in all cases. Finally, an antegrade cardioplegia cannula is placed in the proximal ascending aorta ( Fig. 20.4 ).
